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Post Retirement Benefits - Multiemployer Plans (Details)
 12 Months Ended
Aug. 09, 2016
$ / h
Dec. 31, 2015
USD ($)
Aug. 09, 2015
$ / h
Dec. 31, 2014
USD ($)
Aug. 11, 2014
$ / h
Dec. 31, 2013
USD ($)
Aug. 10, 2013
$ / h
Multiemployer plans:              
Certified zone status, percent funded limit for red status   65.00%          
Certified zone status, percent funded limit for yellow status   80.00%          
Certified zone status, percent funded limit for green status   80.00%          
Multi-employer plan contributions | $ [1]   $ 863,000   $ 719,000   $ 464,000  
Multiemployer plan, postretirement benefit              
Multiemployer plans:              
Maximum percentage of total contribution   5.00%          
Multiemployer plans, collective-bargaining arrangement, maximum hours of work per week for employer contribution   40 hours          
Multiemployer plans, collective-bargaining arrangement, rate of employer contribution     1.35   1.30   1.25
Forecast | Multiemployer plan, postretirement benefit              
Multiemployer plans:              
Multiemployer plans, collective-bargaining arrangement, rate of employer contribution 1.40            
[1] The National Pension Plan utilized a five year amortization extension in accordance with § 431(d) of the Internal Revenue Code of 1986 ("the Code") to amortize its losses from 2008. The plan re-certified its zone status after using the amortization provisions of the Code. The Company's contributions to the plan did not represent more than 5% of total contributions to the plan as indicated in the plan's most recently available annual report for the plan year ended December 31, 2014. Under the terms of the collective-bargaining agreement, the Company is required to make contributions to the plan for each hour worked up to a maximum of 40 hours per person, per week, at the following rates: $1.25 per hour from August 13, 2012 through August 10, 2013